The present invention relates to an eccentric screw pump having a rigid rotor, which is embodied as a spiral, for example a single spiral or helix, and has a circular cross-sectional configuration, and also having a stator that is provided with an elastic or elastomeric lining that delimits an interior space or cavity which accommodates the rotor and has the form of a spiral, for example a double spiral or helix, with a cross-sectional configuration that essentially has the shape of a rectangle bounded on opposite sides by a respective semicircle, whereby the sides of the essentially rectangular portion that interconnect the two semicircles, proceeding essentially from the semicircles, are provided with projections that bulge convexly in a direction toward the interior of the cavity of the stator.
With such a pump (see German Auslegescrift 20 17 670), the convexly bulging or projecting edges result in an increase in the conveying capacity because these edges or sides take into account the fact that the amount of the cavity reduction effected by the sides is approximately proportional to the respectively adjoining thickness of the layer of the elastomeric material of the stator. The greater pressure of the elastomeric material against the rotor caused by the convex surfaces thus reduces the so-called clearance losses and hence increases the pump capacity. Unfortunately, counteracting this advantage is the drawback that the friction losses of the pump increase with an increase of the pressure of the elastomeric material against the rotor, which is particularly disadvantageous for longer pumps of, for example, several meters length.
It is therefore an object of the present invention to eliminate these drawbacks; relatively reduced friction losses should be tolerated without however thereby having to accept greater clearance losses.